The present invention relates to overcenter linkage arrangements and, in particular, to systems for synchronizing door movements with extension movements of equipment contained within the doors.
Overcenter linkage arrangements commonly are used for a variety of purposes dictated usually by the requirements of the situation in which they are used. The present arrangement principally is adapted for aircraft use although other uses also are contemplated. In particular, its function is to extend and retract a large infra-red detector system (IRDS) normally contained or stored in a bay portion of the aircraft behind a pair of clam-shell doors. Conventionally, the IRDS antenna is carried in a fixed, extended and unretractable position. However, for aerodynamic as well as protective reasons, the unretractable arrangements are not too desirable. A preferable arrangement is to provide a protective storage in which the antenna is not exposed to the elements and to possible damage during flight. On the other hand, if the antenna is to be stored, it obviously must be extended for use.
Attempts to provide suitable extension and retraction systems, for one or another reasons, have not been found acceptable. One of the difficulties is that, from an IRDS performance standpoint, it is important that the antenna be held in a firmly secured, stable disposition particularly when extended. Conventional linkage systems permit too much vibration or other movements. However, structural designs also must recognize that aircraft space and weight are at a premium and that strength and stability consequently must be provided in a relatively small and compact manner. Space further dictates a close fit of the antenna and its linkage into the storage area as well as a close fit between the antenna itself and the doors which protectively enclose it. Special care consequently must be taken to assure that the opening and closing movements of the doors do not interfere with the extension and the retraction of the antenna or, in other words, that these movements all are closely and reliably synchronized.
It is known that somewhat comparable circumstances exist in other arrangements. For example, U.S. Pat. Nos. 2,531,263 and 4,014,486, as well as others, disclose systems utilizing overcenter or `lost motion` to synchronize an extension of a loading stairway with the opening of doors behind which the stairway is stored. These prior arrangements, however, are not presently acceptable or, in fact, even adaptable for present purposes. For one reason, their stairways pivot on an axis that is parallel to the pivotal axis of the door so that both members swing outwardly about parallel axes. The present problem is quite different in that the doors swing on an axis that preferably is at a right angle to the pivotal axis of the antenna. Consequently, separate independent linkage assemblies are needed one for the doors and the other for the antenna. Synchronization of such separate and independent assemblies presents a complication both in the retraction as well as the extension movements.
The objects of the present invention should be readily perceivable from the foregoing description. In general, they are achieved by employing, as indicated, separate and independent linkage assemblies for both the antenna and the doors. The linkage assemblies are driven by a common crank shaft which, in turn, is rotatably driven by a rotary actuator. The arrangement is such that the linkage assembly for the doors is driven overcenter when the doors are moved to their fully open position, while the linkage assembly for the antenna is moved overcenter when the antenna is in its fully retracted position. The overcenter disposition of the antenna delays its extension until the doors have partially opened. Also, the overcenter disposition of the doors delays closing until the antenna has been partially retracted. Interference between the two moving objects consequently is effectively eliminated. As another preferred feature, the antenna is locked in a stable position in both its extended and retracted positions. Again, it may be advisable to note that there is no intention to limit the present invention to IRDS systems or, in fact, to the deployment of any particular object whether carried by an aircraft or by some other means.